Pulverizer



Ju 9, 19.45. E. G. B'AILQEY ETAL,

' PULLVERIZER Filed April' 1, 1943 2 Sheets-Sheet 2 IINVTORIJ 'Er'w'n G. 301' BY Gear 83. Ebefso/e A TTORNE Y 1 STATE of carrier air Patented June 19, 1945 PULVERIZER} Ervin G. Bailey, Easton, Pa., and George B."

Ebersole, Akron, & Wilcox Company, tion of New Jersey Ohio, assignors to .TheBabcock' Rockligh; N. J., a corpora-'- Application April 1, 1943, Serial No. 481,388

8 Claims.

The present invention relatesto the construction and-operation of :pulverizers of the type in which materials, such as coal,"phosphate roek, and the like, :are pulverized between oneor more grinding surfaces anda relatively moving rolling grinding element or element and the pulverized material, carried out of the grinding zone in suspension in a gaseous carrier medium. A pulverizerv of this general .type is shown in Schwartz U. 8., Patent No. 2,275,595, in which the pulverizing elements are relatively movable upper and lowerv grindingrings betweenwhich a circular row of grinding balls-is horizontally arranged and the pulverized material removed from the grinding zone byan annular stream of carrier air passing upwardly through an annular throat and picking up pulverized material discharged from the outer circumferentialedge of the lower grinding ring; 1 g y In the operation" of such pulverizers on coal in a direct fire installation, f or. example, the; carrier air serve -as the primary combustion-air and is supplied in a predetermined ratio to the fuel supply. .Where such pulverizer's are used for a relatively wide range of fuel capacity, the amount supplied during-low load operation drops substantially .and the resulting lower velocity usually approaches the minimum velocity required to lift the ulverized material out of the pulverizing zone. In such pulverizers the flow area of the annular'throat is usuallyvproportioned to provide a maximum air velocity at an intermediate portion of the throat sufficient over the designed load range to pick up the normally pulverized material discharged from the outer edge of the lower grinding ring. Normally the space at the outer side, of the lower grinding ring and inthe upper part'of the throat is filled with an air-borne mass ofmaterial from the pulverizing zone held insuspension by the ascending air stream. Oversize and/or high density particles however tend to drop through the throat against the rising air stream and collect in the subjacent section of the pulverizer, from which they are subsequently swept into a trap or compartment ingthe pulverizer base. A the pulverizer load decreases with a consequent decrease in the maximum air velocity in the throat, the dribble of particles from the suspended 'mass through the throat against theliftingeflect of the air stream increases. ;This condition is desirable for the removal of foreign material in the coal, such as pyrites particles, s1ate, -etc., but objectionable and wasteful when the material so tion shown in Fig.

The general object of our invention is the provision of a pulverizer of the type described which ischaracterized by animproved construction and arrangement of the parts formin the throat section of the pulverizer. vA further and more specific object is the provision of an improved pulverizer throat which provides a substantially uniform air velocity therein throughout its height and-circumference and a swirling efiect on the airstream' beyond the throat, while minimizing obstruction or plugging of the throat by descending material.

F The various features of novelty which characterize ourinvention are pointed out with particularityin the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in-which we have illustrated and described a preferred embodiment of our invention. I

Of the drawings:

.Fig. 1 is a sectional elevation of a pulverizer constructed in accordance with our invention;

' Fig. 2 is a plan view of the throat construcity 1 with parts omitted for clar- Fig. 3 is an enlarged view of a portion of the throat shown in Fig. 1

Fig. 4isa fragmentary elevation taken on the line 4-4 .of'Fig. 3;-'and Fig.5 is anplan view'of the parts shown in Fig.4."

The pulverizer illustrated has a substantially cylindrical sectional housing! having a base section II mounted on a foundation l2. The base section contains .the pulverizer drive assembly including a horizontal pinion shaft l3 arranged to drive a vertical drive shaft [4 axially arranged in thehousing. The drive shaft l4 extends upwardly through bearings arranged in a base plate 15. forming the top of the base section II. The upper section I6 of th housing is of substantially cylindrical form anddetachably secured to the'base plate I5. The upper housing section encloses the grinding parts of the pulverizer which comprise a drive yoke *ll of generally conical form keyed on the'upper part of thedrive' shaft l4; and an annular lower grindmgring 19 supported on and dowelled to flattened lower portions of the drive yoke. The upper face ofthe' grinding ring I9 is shaped to form a. track for a'circ'ular row of rolling grinddischarg'ed includesa sizable percentageof coal. ing elements 20,'preferably ball of w t ant alloy steel. The balls support a non-rotary upper grinding ring 2| having a ball track formed in it lower face. An annular spider 22 mounted on the upper ring is provided with lugs 23 arranged in guides on the inner wall of the housing section [6 for preventing rotation, but permitting vertical movement, of the spider and upper grinding ring. A resilient grinding pressure is exerted downwardly on the grinding parts by a number of coil springs 24 engaging the spider.

The material to be pulverized is supplied through a feed spout 25 to the inner side of the upper grinding ring and ball row and falls on the inclined upper surface of the drive yoke ll, being distributed throughout the grinding area by the rotation of the drive yoke and'associated parts. The material flows outwardly over the upper surfac of the yoke and lower grinding ring, is pulverized between the relatively moving balls and grinding rings, and discharges over the outer edge of the lower grinding ring 19 at surrounding the lower part of the housing section IS. The stream of carrier air from the annular wind box passes into thepulverizer housing section [6 through passages 33 in the housing at the outer sid of the drive yoke. The air stream then flows upwardly through an annular throat passage 34 formed between the outer side of the lower grinding ring l9 and an annular sectional throat plate 35 mounted for.

adjustment radially onthe inner side-of the housing section IS. A portion/of the throat ring is formed by a segmental a pivoted. relief gate 35 which swings out to permit the passage of any large pieces of unpulverizable or foreign material, such as tramp iron, into the lower portionof the housing. At a pointsubsequent to the relief gate 36 in direction of rotation, the

base section of the housing is provided with a I all of material not swept up by the air stream due to their excessive size or density fall through the subjacent part of the air throat or through the relief gate section thereof into the air entrance area at the outer side of the drive yoke.

In coal pulverizers of the character described previously used in a direct firing system, the amount of primary or carrier air supplied is substantially directly proportional to the amount of coal to be pulverized. The air velocity in the throat 3 will correspondingly vary over a relatively wide range with corresponding changes in pulverizer load. Accordingly, in the lower part of the load range, the air velocity in the throat '34 may be close to the minimum velocity necessary to lift the pulverized material out of the pulverizing zone. This condition is complicated by the presence of a mass of pulverized material at the outer side of the ball row and above the throat which is maintained in a floating condition by the rising air stream. The heavier parts of the mass tend to drop into the throat and either clog a portion of the same or fall throughinto the lower part of the casing. In the lower part of the pulverizer load range, the amount of material dribbling down through the throat may reach such proportions that a substantial increase in the operating costs will result. For that reason and to avoidoutages due to the pulverizer becoming plugged, the dribble should desirably be eliminated or restricted to a low value throughout the entire load range of th pulverizer.

In accordance with our invention, the parts defining the throat passage 34 are constructed and relatively arranged to provide air flow conditions therethrough which will restrict dribbling of material through the throat to a minimum throughout the designed load range of 1 the pulverizer. For this purpose the throat compartment 40 for the collection of material dropplng through the throat 34 including the gate section 36 into the lower part of the hous-v ing. The compartment 40 communicates 'with the grinding zone through a small opening in the housing base plate l5 below which a slidable gate 42 is mounted and manually operable through a rack and pinion system 43 to open and close the opening ll. The compartment 40 is periodically cleaned through a door.

'In the operation of the pulverizer construction illustrated, the material to be pulverized is supplied to the inner side of the. grinding elements and pulverized during its outward pas sage therethrough. The pulverized materialflows forwardly over the outer edgeof the lowergrinding ring in the direction of rotation of the ring. The pulverized material is then picked up by the annular air stream flowing upwardly through the air throat, the material-laden air passing upwardly to the classifier 30 which sepa-- rates the coarse and fine particles, the coarse particles being returned to the inner side of the ball row and the fine particles delivered'to the pulverizer outlet or outlets 3!. The particles plate 35 is formed with an upper surface'iiii inclined outwardly at an angle of approximately 45 from a point slightly above the level of the surface of the lower grinding ring. The outer side l9 of the lower grinding ring slopes out- Wardly at a slight angle to the vertical, while the throat plate has a fiat surface 35 at a downwardly diverging angle opposite tothe ring surface l9. This downward divergence of the opposite relatively moving sides of the throat facilitates the elimination of anyrpieces of material lodging in the upper part of the throat. Once such material is Worn by the relatively moving parts enough to pass the upper end of throat, it is free to drop through the remainder of the throat. g

The throat is subdivided circumferentially by a series of circumferentially'spaced lugs or crickets 50 on the face 35 of the throat plate and extending substantially the full height of the throat. The lugs 50 are uniformly spaced circumferentially and shaped to define sloping air passages 5| therebetween of substantially uniform cross-sectional area .throughout the height or effective flow length thereof, whereby the rising air-stre-am' will have a constant velocity throughout the throat at any givenfload. For this purpose each log is shaped. to compensate I for the divergence of the surfaces l9 and 35 as well as to effect a swirling of .the rising air stream beyond the throat, By sloping the lugs and thereby the air passages it the length of the passage relative to height-is advantageously increased and the air streams are givena direc terial in which? the maximum lifting. efiect thereon isexerted.v Each lug progressively increases in cross-sectional area downwardly, having opposite faces 50 and 50% arranged at different angles; .Th'eslope of these: faces may be varied ,to some extent, but by wayof example, the face .50, is'shown at an angl e-of 35 and theface 50 at. an angle of 55 to-the horizontal. Thefaces .50 and 50 are alsoarranged at an angle to the to 'carryaway pulverized material in suspension,

"andmeans mounted in said throat and arranged stricted throat 34. Onreaching the throat .it is subdividedby the lugs or crickets 50' into a multiplicity of parallel streams, each. Of-WhiCh'iSfdirected upwardly at an. oblique angle through the corresponding throat passage 5|. Thisdirection of the air streams bringsthem into'a posi- .tion. behind the discharging coal particles, from the grinding zone, avoiding the turbulence and I loss of energy which tend tooccur when an air stream cuts. acrossa stream of dischargingcoal. The maximum theoretical lifting effect is closely approached and the coal-laden airstreamsreunite'at thetop of the. throat and pass'upwardly to the classifier.

It has been found that the dribble is substantially reduced in amount and changed in character with the described throat construction.

With this constant velocity throat very little fine material is present in the dribble and those fines aregenerallypyrites or slate. The, provision of aconstant velocity. over the fullheight: or flow length of the throat provides the necessary time factor required to subject the descending particles to the naximum lifting effect of the air stream and thus increases its efiectiveness at any given velocity. It also provides an improved winnowing effect on the descending particles of material, resulting in better separation. of the coal and foreign material.

While in accordance with the provisions of the to: subdivide said throat into a plurality of cir- :cumferentially adjacent passages of substantially constant: cross-sectional flow .area- .throughout theirheight. 1 x w 2. Apulverizer comprising a closed casing, a grinding member mounted Withinthe casing" for rotation about a central vertical" axis, a plurality of rolling grinding elements in contact with said rotary: grinding member means for introducing material .tobe ground between said rotary grinding membe'r and grinding elements, there being'an annular air throat of varying width between the "outer side of said rotary grinding member and the enclosing wall of said casing, means for introducing air upwardly through said throat to carry away pulverized material insuspension, and means mounted in said throat and arranged to subdivide said throat into a plurality of circumferentially adjacent passages of substantially constant cross-sectional flow area throughout their height and arranged the invention covered by our claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features. In general, our invention is equally applicable to any pulverizer in which the pulverized material is discharged from the edge of rotating grinding part into an ascending air,

stream. In the claims, the word "air is intended to generically cover any gaseous carrier medium suitable for removing pulverized material in the manner described.

We claim:

1. A pulverizer comprising a closed casing, a grinding member mounted within the casing for rotation about a central vertical axis, a plurality of rolling grinding elements in contact with said rotary grinding member, means for introducing material to be ground between said rotary grinding member and grinding elements, there being an annular air throat of varying width between the outer side of said. rotary grinding member and the enclosing wall of said casing, means for introducingair' upwardly through said throat ing combustion air upwardly through said throat to carry-away pulverized coal in suspension, means for collecting and withdrawing from the lower-portion ofsaid casing material falling through said throat, and means mounted'in' said throat and arranged to subdivide said throat into a plurality of circumferentially adjacent passages of substantially constant cross-sectional flow area throughout their height.

'4. In a direct-fired fuel burning system, a pulverizer comprising a closed casing, a grinding member mounted within the casing for rotation about a central vertical axis, a plurality of rolling grinding elements in contact with said rotary grinding member, means for introducing coal to be ground between said rotary grinding member and grinding elements, there being a downwardly diverging annular air throat between the outer side of said rotary grinding member and the enclosing wall of said casing, means for introducing combustion air upwardly through said throat to carry away pulverized coal in suspension, means for collecting and withdrawing from the lower portion of said casing material falling through said throat, and means mounted in said. throat and arranged to subdivide said throat into a plurality of circumferentially adjacent passages of substantially constant cross-sectional flow area throughout their height and arranged to direct an air flow therethrough swirling in the direction of rotation of the adjacent portion of said rotary grinding member.

throat plate radially spaced irom said grinding ring to define an annular throat therebetween throat into a. plurality oicircumferentially adjacent passages of substantially constant crosssectional flow area throughout their height.

6. A pulverizer comprising a closed casing, a grinding ring mounted within the casing for rotation about a central vertical axis, a plurality of grinding balls on said grinding ring, means for introducing material to be ground between said rotary grinding ring and grinding elements, an annular throat plate radially spaced from said grinding ring to define an annular air throat therebetween receiving pulverized material discharged from said grinding ring, means for introducing air upwardly through said throat to carry away pulverized material in suspension, means for collecting and withdrawing from the lower portion of said casing material falling through said throat, and means in said throat mounted on said throat plate and arranged to subdivide said throat into a plurality of circumferentially adjacent passages arranged to direct on air flow therethrough swirling in the direction of rotation of the adjacent portion of said grindincrin 7. A pulverizer comprising a closed, casing, a

grinding ring mounted within the casing, a plurality of grinding balls on said grinding ring, means for effecting relative movement between said grinding balls and grinding ring, means for introducing material to be ground between said grinding ring and grinding elements, an annular grinding ring and grinding elements, an annular throat plate radially spaced from said grinding ring to define an annular air throat therebetweenhaving a pair of downwardly diverging opposite sides and receiving pulverized material dis charged from said grinding ring, means for introducing air upwardly through said throat to carry away pulverized material in suspension, means for collecting and withdrawing from the lower portion of said casing material falling through said throat, and means in said throat mounted on said throat plate and arranged to subdivide said throat into a plurality of circumferentially adjacent passages of substantially constant cross-sectional now area throughout their height and arranged to direct an air flow 'therethrough swirling in the direction of discharge of pulverized material from the adjacent portion of said grinding ring.

8. A pulverizer comprising a. closed casing, a

grinding ring mounted within the casing for rotation about a central vertical axis, a plurality of grinding balls on said grinding .ring, means for introducing material to be ground between said rotary grinding ring and grinding elements, an annular throat plate radially spaced from said grinding ring to define an annular air throat therebetween having a pair of downwardly diverging opposite sides and receiving pulverized material discharged from said grinding ring, means for introducing air upwardly through said throat 

